Mayor Rahm Emanuel wants to put a long standing Chicago practice on the books to ensure that police detain only undocumented immigrants who are suspected or convicted criminals.

The symbolic ordinance Emanuel proposed Tuesday would allow city police to turn over to federal agents undocumented immigrants who are wanted on a criminal warrant or who have been convicted of a serious crime, but not others.

Chicago has practiced a sanctuary city policy dating back to Mayor Harold Washington’s tenure during the 1980s. City agencies have been prohibited from inquiring about the immigration status of people requesting services. The Chicago Police Department also refrains from questioning victims of crime, witnesses or other law-abiding residents about their legal status.

Police, however, do run background checks on people suspected of committing crimes. In recent years, if officers found a deportation order, the U.S. Immigrations and Custom Enforcement expected police to turn over undocumented immigrants. But the city had no specific requirement about how to act in those cases, and the policy was inconsistently enforced, according Adolfo Hernandez, the director of the Mayor’s Office of New Americans.

The police department does not exist to serve as an “adjunct for the immigration service,” Emanuel said.

“We’re not going to turn people over to ICE and we’re not going to check their immigration status, we’ll check for criminal background, but not for immigration status,” Emanuel said at a news conference at Little Village High School.

Officials with the federal immigration agency could not be reached for comment.

The announcement gave Emanuel the opportunity to steer the conversation away from Chicago’s rising violent crime rate, at least for a day. Emanuel’s stance puts Chicago in sharp contrast to states such as Arizona and South Carolina, where police are required to check the immigration status of people they stop.

Standing by the mayor’s side was U.S. Rep. Luis Gutierrez, who has been at odds with Emanuel on immigration issues. Gutierrez, who considered running in last year’s mayoral contest, has said that as chief of staff for President Barack Obama, Emanuel obstructed comprehensive immigration reform because it would hurt Democrats at the polls.

While the issue separated the two in the past, it was the thing that united them on Tuesday, Gutierrez said.

“This isn’t a question of cuddling up to criminals. We detest, hate and want ourselves rid of criminals,” Gutierrez said. “If you’re a drug dealer, if you’re a gang member, if you’re a murderer or rapist, if you’re a bad person I want the immigration system to rid you of our society as quickly as efficiently, fast, yesterday, I want you gone.

“If you’re working hard, if you’re sweating and toiling and raising your family and the immigration system is broken and has not allowed you to participate and integrate yourself fully, then I want us to stand back.”

While Chicago largely prohibited police from assisting federal agents in an investigation of citizenship or immigration status, immigration rights advocates said there have been instances when police cooperated with ICE.

The Illinois Coalition for Immigrant and Refugee Rights cited the case of Rose Tchakounte, a Cameroon immigrant who the advocacy group said was arrested during a February traffic stop and spent two nights in custody after police discovered she had an outstanding deportation order. When federal agents failed to pick her up, Chicago police delivered her to ICE, the group said.

“Making sure that our city’s law enforcement resources are focused on serious crimes that harm immigrants and natives alike, and that immigrants and their families are not subjected to racial profiling, will strengthen the relationship between Chicago police and immigrant communities and make our entire city safer,” said Lawrence Benito, the immigration group’s chief executive officer.

Emanuel is expected to introduce the ordinance at the July 25 City Council meeting.